Previously, many types of concrete pipes have been developed in endeavoring to provide an effective means to pre-stress the concrete employing a metallic reinforcement or a pressurized solidifying compound for compression.
The prior art listed below did not disclose patents that possess any of the novelty of the instant invention; however the following U.S. patents are considered related:
Pat. No.InventorIssue Date3,982,565IidaSep. 28, 19764,153,656BunyanMay 8, 19794,771,530CreedonSep. 20, 19884,840,200CreedonJun. 20, 19895,065,795CreedonNov. 19, 19915,928,447GianFransiscoJul. 27, 19996,076,562KuoJun. 20, 20006,155,810ThimDec. 5, 20006,123,485Mirmiran et al.Sep. 26, 2000
Iida in U.S. Pat. No. 3,982,565 teaches a method of pre-stressing a concrete pipe by arranging a reinforcing cage in a form and cast expansive concrete within the form such that the reinforcing cage is disposed outwardly of the center of the wall thickness of the concrete layer and then centrifugally forming the pipe.
U.S. Pat. No. 4,153,656 issued to Bunyan is for a method of joining pipes in which a sleeve is placed over the adjacent ends of the pipes to overlap each pipe. The sleeve fits with clearance around the pipe ends. The ends of the clearance space are closed by inflating hollow sealing rings and then epoxy resin is injected into the clearance space. The pressure of the epoxy resin is then raised to a substantially greater pressure than atmospheric with the pressure maintained until the resin sets.
Creedon in U.S. Pat. No. 4,771,530 discloses a method of pre-stressing concrete members using a pressure containing casing positioned around the outside surface leaving a cavity therebetween. A pressurized medium is injected into the cavity at a pressure sufficient to apply the required pre-stress force. The pressurized medium changes form by hardening after injection which includes grout, thermoset plastic and epoxy resin. When the concrete member is cast, a cavity is formed by peeling the concrete member and casing away from each other as the medium is injected.
U.S. Pat. No. 4,840,200 of Creedon teaches a pre-stressed tube having inner and outer walls with an intermediate non-adhering lamina layer. A pressure medium is fluidically injected within the lamina layer and after hardened provide a pre-stress force forming a permanent leak-proof pre-stress force to the tube.
U.S. Pat. No. 5,065,795 issued to Creedon is for a pre-stressed concrete article including overlaying the end of the article and having a gasket ring between the article and the end walls. A hardenable medium is injected between the jacket and the concrete article and generates a sufficient pressure so as to outwardly bulge the jacket, drawing the end walls together thereby compressing the gaskets.
Kuo's U.S. Pat. No. 6,076,562 is my previous patent which disclosed a pre-stressed concrete pipe rolled inside a steel cylinder with a seal joint at each end of the pipe between the pipe outside surface and the inner wall of the steel cylinder. The seal joint incorporates an annular groove to distribute hardenable medium fluid injected from holes through the steel cylindered wall. The fluid penetrates the entire boundary surface between the concrete and the steel pipe under pressure forcing the concrete into compression while the steel cylinder expands outwardly. The seals at the pipe ends prevent the medium from leaking. When the fluid reaches a desirable pressure a check valve on the supply line retains pressure in the pipe while the fluid supply stops. The pipe retains its compression after the medium is hardened.
U.S. Pat. No. 6,123,485 issued to Mirmiran et al. is for fiber reinforced plastic formed about concrete piles and columns which include an extruded shell with interior protruding portions. The concrete filled tubes are enhanced by pre-stressing the concrete core increasing the bond with the tube and placing the tube in an active hoop tension.
For background purposes and as indicative of the art to which the invention is related reference may be made to the remaining cited U.S. Pat. No. 5,928,447 issued to GianFransisco and U.S. Pat. No. 6,155,810 of Thim.